1. Field of the Invention
The present invention relates to an image forming apparatus, which can in form a plurality of identical images in parallel.
2. Description of the Related Art
As an image recording apparatus, a copying machine, an LBP, and the like are popularly used. Recently, a color copying machine for reproducing a full-color original image in full color is proposed as well.
Such a color copying machine has an image transfer member such as a transfer drum, and normally forms a color image by sequentially overlaying magenta, cyan, yellow, and black color-separated images on a recording sheet held on the transfer member.
Upon formation of a plurality of images in such a color image recording apparatus, an arrangement for attaching a plurality of recording sheets onto a transfer drum, and recording identical color images on the attached recording sheets is proposed (U.S. patent application Ser. No. 437,033, and the like). For example, when two recording sheets are attached to the transfer drum, an optical system is driven twice to record two magenta images, and thereafter, the optical system is driven twice each for cyan, yellow, and black recording colors, thereby forming two each color images.
More specifically, since the optical system performs a read scanning operation in units of recording sheets attached to the transfer drum, the optical system must be returned to the read scanning start position in the interval between the trailing end of a recording sheet and the leading end of the next recording sheet on the transfer drum.
In the above-mentioned apparatus, when a plurality of recording sheets are attached to the transfer drum, and the optical system is to be returned to a home position in the interval between the adjacent recording sheets, the return speed becomes higher than that in an original reading mode.
As a result, when image formation is to be performed at higher speed, the reading optical system cannot be returned in the interval between the adjacent recording sheets due to a mechanical limitation on the driving speed.
When given image formation efficiency is to be maintained while returning the optical system at relatively high speed, the return time of the optical system must be assured by increasing the interval between recording sheets. As a result, the diameter of the transfer drum must be increased, and the apparatus size becomes large. Even if the high-speed image formation is attained in this manner, since the time required for completing one revolution of the transfer drum is increased due to an increase in diameter of the transfer drum, the copy speed cannot be so increased.